1. Field of the Invention
The invention relates to optical fiber and methods of manufacturing optical fiber. More particularly, the invention relates to optical fiber coatings and methods of coating optical fibers.
2. Description of the Related Art
High performance communications systems, i.e., those systems having gigabit transmission speeds, are being made possible by improving the bandwidth of optical fiber. However, achieving those desired transmission speeds in multimode fiber has been hindered by problems such as dispersion. Because multimode optical fibers are capable of propagating more than one mode of optical energy, an inherent problem with dispersion exists. Such dispersion, more specifically known as modal dispersion, is the broadening or spreading of an optical energy output pulse caused by delays resulting from various pulse modes traveling through the optical transmission medium at different speeds. Such dispersion can be managed by mode mixing or mode coupling, i.e., the mixing or scrambling of the various modes in such a way that effectively reduces the difference in travel times of the various pulses modes. The reduction in dispersion improves the bandwidth of the multimode optical fiber.
It has been recognized that certain microbending (i.e., microscopically small deviations in the fiber axis) of multimode fiber often causes advantageous mode coupling or mode mixing. That is, the introduction of perturbations in the multimode cladding modes enhances mode coupling. Conventional approaches to inducing microbending has varied from externally inducing bends in the outer regions of the fiber (see, e.g., U.S. Pat. No. 4,038,062, which is co-owned with this application) to internally applying refractive index perturbations in the optical fiber preforms that subsequently are drawn into optical fibers (see, e.g., U.S. Pat. Nos. 5,867,616 and 5,613,028). Many conventional methods for inducing microbending techniques have had difficulty in controllably introducing perturbations and reliably reproducing the desired microbends. Furthermore, many conventional microbending techniques are undesirable from the standpoint of manufacturing cost and efficiency.
Accordingly, there remains a need for controllably inducing microbends in optical energy transmission medium such as optical fibers to enhance mode coupling therein.